1. Field of the Invention
The present invention relates to a raveling-preventing agent for a glass fiber woven fabric. The raveling-preventing agent of the present invention is preferably used for preventing the marginal raveling and the margin of a glass fiber woven fabric which is produced by means of an air-jet loom, etc., and used for producing a copper-clad laminate.
2. Prior Art
A glass fiber woven fabric has been mostly produced by means of a shuttle loom, while it is recently increasingly produced by means of a shuttleless loom such as an air-jet loom. In the field of copper-clad laminates where a large amount of glass fiber woven fabrics are used, nearly all of the glass fiber woven fabrics are produced by means of an air-jet loom. When an air-jet loom is used, the weft is cut every time when it is allowed to run from edge to edge across a fabric to be produced. As a result, a loose marginal portion of the weft yarns is present in each of the side portions of the fabric (the term "loose marginal portion" is also called "feathered edge"). As is well known, a glass fiber woven fabric for a copper-clad laminate is impregnated with a varnish of a thermosetting resin such as an epoxy resin and dried to prepare a prepreg. A plurality of the so-prepared prepregs were stacked, copper foil(s) is/are stacked, and heat and pressure are applied to obtain a copper-clad laminate.
When a prepreg is prepared from a glass fiber woven fabric having feathered edges, produced by means of a shuttleless loom such as an air-jet loom, the following problems occur.
The first problem is that since the feathered edges of a glass fiber woven fabric contain an excess of a resin, the feathered edges tend to have a larger thickness than any other portion. When a prepreg having a larger thickness in the feathered edges as described above is cut to a predetermined size and stacked, the resultant stack has a larger thickness in a place where the above feathered edges are present together, and the stack is consequently not entirely uniform in thickness. The above prepreg stack which is not uniform in thickness across the entirety of its width causes a variety of disadvantages when used for producing a product. For example, when a copper-clad laminate is produced from such a prepreg stack, there is a defect in that the prepreg stack cannot be pressed in the entirety of its width.
The second problem is that when the form of each edge of the prepreg is viewed along its length, each edge does not have a linear form, but has an uneven form due to the feathered edges. When the prepreg whose edges have an uneven form is cut to a predetermined size and stacked, there is a defect in that it is difficult to bring the edge of the marginal portions in line. Further, when the edges of the marginal portions are brought in line, the uneven edge portions are partially cut or broken to pieces and the resulting pieces are spattered to be included in the prepreg, which inclusion causes defective products.
The third problem is that when a prepreg is produced, the loose marginal portions of a glass fiber woven fabric are partially cut or broken and the resulting pieces are included in a varnish and adhere to the prepreg surface, which ends up in defective products.
When a prepreg is prepared from a glass fiber woven fabric having loose marginal portions, the foregoing problems arise, while the above first problem similarly occurs concerning the marginal portion of a glass fiber woven fabric produced by means of a shuttle loom.
For avoiding the first and second problems, there may be employed a method in which the marginal portion is removed by cutting it off from the produced prepreg. In this case, however, the third problem cannot be avoided. Further, the yields of the glass fiber woven fabric and varnish decrease, which is costwise undesirable.
Further, there may be employed a method in which the marginal portion of a glass fiber woven fabric is removed before the prepreg is prepared from the glass fiber woven fabric, and some proposals have been made. For example, there is a method in which the loose marginal portion is cut off by melting it with laser light while the remaining end portion is simultaneously bound. There is also a method in which yarns of a thermoplastic resin are incorporated as marginal portions of part of warp yarns for a glass fiber woven fabric and the yarns of a thermoplastic resin are fused after the glass fiber woven fabric is produced. However, the method using laser light has not yet been put to practical use, since it has problems in that the cutting rate by melting cannot be increased and that the melting drip of small balls in a varnish occurs at a prepreg step. The problem with the method of incorporating yarns of a thermoplastic resin as marginal portions is that this method can be applied only to a special woven fabric, since the general step of heat cleaning for producing a glass fiber woven fabric cannot be carried out.
Further, it has been proposed to apply a hot-melt adhesive to the marginal portion of a glass fiber woven fabric for overcoming the above problems. Since, however, a glass fiber woven fabric is heated around a temperature of 150.degree. C. in a prepreg step while the hot-melt adhesive contains a solvent, warp yarns of the marginal portion ravel under some conditions to cause a trouble of being caught in a roller of a prepreg apparatus. Further, there is another problem: The marginal portions to which the hot-melt adhesive has been applied are thicker to some extent, and when the produced prepreg is cut to a predetermined size and stacked, the prepreg stack has a larger thickness in the marginal portions than in the central portion, which thickness difference hinders the automation of a lamination step.